cis‐Specific Living Polymerization of 1,3‐Butadiene with CoCl2 and Methylaluminoxane

The polymerization of 1,3‐butadiene was conducted by CoCl₂ combined with methylaluminoxane (MAO) as a cocatalyst at 0 and 18°C. The uni‐modal molecular weight distribution curves of the resulting polymers shifted toward higher molecular weight regions and became narrower when increasing the polymerization time. The number‐average molecular weight increased linearly with polymerization time, while the polymer yield increased exponentially in the initial stage. As a consequence, the number of polymer chains, calculated from the polymer yield and M̄_n, increased gradually with polymerization time to reach a plateau value. These phenomena was interpreted based on a slow initiation system without any termination and chain transfer reaction. The microstructure of the polymer was determined by ¹H NMR and ¹³C NMR spectroscopy to be a cis‐1,4 structure in a 98–99% purity.     

Effects of halogen ligands on 1,3‐butadiene polymerization with cobalt dihalides and methylaluminoxane

We conducted 1,3‐butadiene polymerization at 0 and 18 °C using CoX₂ (X = halogen) combined with MAO to elucidate the role of halogen ligands attached to cobalt. With increasing the polymerization time, the molecular weight distribution curves of the polymers obtained progressively shifted to higher molecular weight regions accompanied by narrowing polydispersity, irrespective of the cobalt halides employed. The polymer yield linearly increased after an exponential induction stage, while the number‐average molecular weight linearly increased vs. polymerization time. Thus, the number of polymer chains calculated from the polymer yield and the number‐average molecular weight increased with polymerization time. After a certain polymerization time, the number of polymer chains was saturated to be about 60% catalyst efficiency in the CoCl₂ and CoBr₂ systems but only about 2% in the CoI₂ system. The number‐average molecular weight increases linearly vs. polymer yield from a small positive intercept. These phenomena were interpreted by a slow initiation system without any termination and chain transfer reaction. The kinetic analysis indicated that the rates of initiation were significantly influenced by the nature of the halides and descended in the following order, CoCl₂ > CoBr₂ > CoI₂ > CoF₂ = 0, whereas the rates of propagation were independent on variation of halogen ligands. ¹H and ¹³C NMR analyses of the polymers indicated that the microstructure of the resulting polymer was high cis‐1,4 irrespective of the halogen ligands.

The number of polymer chains of CoI₂ as a function of polymerization time.     

Novel Methylaluminoxane‐Activated Neodymium Isopropoxide Catalysts for 1,3‐Butadiene Polymerization and 1,3‐Butadiene/Isoprene Copolymerization

The homo‐ and copolymerizations of 1,3‐butadiene and isoprene are examined by using neodymium isopropoxide [Nd(Oi‐Pr)₃] as a catalyst, in combination with a methylaluminoxane (MAO) cocatalyst. In the homopolymerization of 1,3‐butadiene, the binary Nd(Oi‐Pr)₃/MAO catalyst works quite effectively, to afford polymers with high molecular weight ( ≈ 10⁵ g mol^‐1), narrow molecular‐weight distribution (MWD) (/ = 1.4–1.6), and cis‐1,4‐rich structure (87–96%). Ternary catalysts that further contain chlorine sources enhance both catalytic activity and cis‐1,4 selectivity. In the copolymerization of 1,3‐butadiene and isoprene, the copolymers feature high , unimodal gel‐permeation chromatography (GPC) profiles, and narrow MWD. Most importantly, the ternary Nd(Oi‐Pr)₃/MAO/t‐BuCl catalyst affords a copolymer with high cis‐1,4 content in both monomer units (>95%).

     

Polymerization of 1,3‐Butadiene Initiated by Neodymium Versatate/Diisobutylaluminium Hydride/Ethylaluminium Sesquichloride: Kinetics and Conclusions About the Reaction Mechanism

The kinetics of the polymerization of 1,3‐butadiene initiated by the ternary Ziegler–Natta catalyst system comprising neodymium versatate (NdV), diisobutylaluminium hydride (DIBAH) and ethylaluminium sesquichloride (EASC) have been studied in order to quantify the impact of the catalyst components EASC and DIBAH on the polymerization rate, the control of molar masses, the molar mass distributions as well as on the microstructure of the resulting polymer (cis‐1,4, trans‐1,4 and 1,2 content). A further focus of the work was on the elucidation of the living nature of the polymerization. It has been found that the catalyst component EASC influences the reaction rate and the microstructure of the obtained polybutadiene. The main effect of the variation of DIBAH is on the molar mass, but the polymerization rate and the microstructure are also influenced. Straight lines are obtained for the dependence of the molar masses on monomer conversion revealing the living nature of the polymerization. The theoretically predicted molar masses are significantly higher than those experimentally found. This discrepancy is explained by the existence of dormant species resulting from the reversible transfer of living polymer chains from Nd onto Al. Only one third of the DIBAH which is not consumed by the processes of scavenging of impurities and activation of the Nd catalyst, is involved in this transfer reaction. This makes DIBAH an inefficient chain control agent for the experimental conditions applied (namely 60°C). A reaction scheme is put forward which accounts for the features observed.     

Living Anionic Polymerization of 4‐Trimethylstannylstyrene

The living anionic polymerization of 4‐trimethylstannylstyrene in tetrahydrofuran at ?78 °C, initiated with sec‐butyllithium, is achieved for the first time. Unwanted side reactions, such as the nucleophilic attack of a carbanion to the stannyl group, may be suppressed through the equimolar addition of dibutylmagnesium (Bu₂Mg) to the initiator. The suppression of side reactions allows the control of the molecular weight of poly(4‐trimethylstannylstyrene) and maintains low molar‐mass dispersity (?_M) values of less than 1.1. By increasing the feed ratio of the monomer to the initiator, the molecular weight increases proportionally, indicating a highly controllable polymerization reaction. Controlled syntheses of block and statistical copolymers derived from styrene and 4‐trimethylstannylstyrene are successfully developed due to the similar nucleophilicity of their living chain termini.     

Living Metathesis Polymerization of Diethyl Di‐2‐butynyl Malonate by Molybdenum‐Based Ternary Catalysts

The living polymerization of diethyl di‐2‐butynyl malonate (DEDBM) was achieved with a MoOCl₄‐based ternary catalyst, MoOCl₄—Bu₄Sn—EtOH, to give a polymer with five‐ and six‐membered rings in the main chain. In contrast, the polymerization of diethyl dipropargyl malonate (DEDPM) with the same catalyst led to gelation. Block copolymers were obtained from DEDBM and other substituted acetylenes such as 1‐chloro‐1‐octyne. Poly(DEDBM) forms a condensed monomolecular membrane at the air–water interface.     

Polymerization of Propene and 1,3‐Butadiene with Vanadyl(V) Monoamidinate Precatalysts and MAO or Dialkylaluminum Chloride Cocatalysts

Summary: Two new vanadyl(V) amidinates have been synthesized and characterized by single crystal X‐ray diffraction and ¹H NMR. The complexes are dimeric with Cl bridges and monodentate coordination of the amidinate ligand to pseudooctahedral vanadium. In the presence of organometallic compounds of aluminum, these vanadyl complexes promote polymerization of propene and 1,3‐butadiene.

     

Pseudo‐Living Anionic Telomerization of Buta‐1,3‐diene

Low‐molecular‐weight liquid polybutadienes (1 000–2 000 g · mol^?1) consisting of 60 mol‐% poly(buta‐1,2‐diene) repeating units were synthesized via anionic telomerization. Maintaining the initiation and reaction temperature at less than 70 °C minimized chain transfer and enabled the polymerization to occur in a living fashion, which resulted in well‐controlled molecular weights and narrow polydispersity indices. MALDI‐TOF mass spectrometry confirmed that the end groups of liquid polybutadienes synthesized via anionic telomerization contained one benzyl end and one protonated end. In comparison, the end groups of liquid polybutadienes synthesized via living anionic polymerization contained one sec‐butyl or butyl end and one protonated end.

     

Fiber‐Like Micelles from the Crystallization‐Driven Self‐Assembly of Poly(3‐heptylselenophene)‐block‐Polystyrene

The crystallization‐driven self‐assembly (CDSA) of crystalline‐coil polyselenophene diblock copolymers represents a facile approach to nanofibers with distinct optoelectronic properties relative to those of their polythiophene analogs. The synthesis of an asymmetric diblock copolymer with a crystallizable, π‐conjugated poly(3‐heptylselenophene) (P3C7Se) block and an amorphous polystyrene (PS) coblock is described. CDSA was performed in solvents selective for the PS block. Based on transmission electron microscopy (TEM) analysis, P3C7Se₁₈‐b‐PS₁₂₅ formed very long (up to 5 μm), highly aggregated nanofibers in n‐butyl acetate (nBuOAc) whereas shorter (ca. 500 nm) micelles of low polydispersity were obtained in cyclohexane. The micelle core widths in both solvents determined from TEM analysis (≈ 8 nm) were commensurate with fully‐extended P3C7Se₁₈ chains (estimated length = 7.1 nm). Atomic force microscopy (AFM) analysis provided characterization of the micelle cross‐section including the PS corona (overall micelle width ≈ 60 nm). The crystallinity of the micelle cores was probed by UV–vis and photoluminescence (PL) spectroscopy and wide‐angle X‐ray scattering (WAXS).     

Synthesis of Propylene/1‐Butene Copolymers with Ziegler‐Natta Catalyst in Gas‐Phase Copolymerizations, 1

Summary: The appropriate choice of comonomers can be used to create a wide range of polymer properties, leading to considerable improvement of product performance. Experimental runs were performed to evaluate the effect of 1‐butene on the crystallinity, the melt temperature and the molecular weight distribution (MWD) of the final propylene/1‐butene copolymer resins. According to the results obtained, the melt temperature of the copolymer material can be reduced significantly compared to that of the polypropylene homopolymer. The incorporation of 1‐butene into the copolymer chain leads to a decrease of the sealing initiation temperatures of propylene polymer resins. GPC analyses of copolymer samples showed that 1‐butene concentration does not seem to significantly influence either the shape of the MWD or the polydispersity indexes for a given set of reaction conditions. Therefore, a family of propylene/1‐butene random copolymers grades can be successfully developed for gas phase processes for packaging and film applications.

     

Functionalization and Linking Chemistry of Poly(styryl)lithium with 1,3‐Butadiene Diepoxide

Summary: The reaction of excess poly(styryl)lithium ( = 1 400 g · mol^?1) with 1,3‐butene diepoxide proceeds efficiently to produce a coupled product with two in‐chain hydroxyl groups. The pure coupled, functionalization product was isolated in quantitative yield by silica gel column chromatography. This product was characterized by ¹H and ¹³C NMR spectroscopic analyses, as well as MALDI‐TOF mass spectrometry. The DEPT ¹³C NMR spectrum showed that a disecondary 1,2‐diol unit was present, consistent with attack of PSLi on the least‐substituted, methylene carbons of 1,3‐butadiene diepoxide. The MALDI‐TOF mass spectrum of the purified product exhibited only one distribution with monoisotopic peaks corresponding to the coupled, dihydroxy‐functionalized polystyrene.

MALDI‐TOF mass spectrum of the purified, in‐chain, hydroxyl‐functionalized polystyrene and the reaction of PSLi with 1,3‐butadiene diepoxide.     

Stereochemical Pseudohexad 13C NMR Resonances and Regioregular Propylene/Ethylene‐1‐13C Copolymers

This paper reports the assignment of the ¹³C NMR resonances of the S_ββ and S_αγ methylenes observed in the spectra of copolymers of propylene with trace amounts of enriched ethylene‐1‐¹³C. The assignment is achieved by comparing the chemical shifts calculated by an empirical method (at the CH₂ stereochemical pseudohexad level), with the experimental spectra of regioregular copolymers with different stereochemical structure. The implications of the observed S_ββ and S_αγ resonances on the stereochemical polymerization mechanisms are also discussed.

     

Successive Synthesis of Multiarmed and Multicomponent Star‐Branched Polymers by New Iterative Methodology Based on Linking Reaction between Block Copolymer In‐Chain Anion and α‐Phenylacrylate‐Functionalized Polymer

A series of multiarmed and multicomponent miktoarm (μ‐) star polymers have been successfully synthesized by developing a new iterative methodology based on a specially designed linking reaction of the block copolymer in‐chain anions, whose anions are positioned between the blocks, with α‐phenylacrylate (PA)‐functionalized polymers. The iterative methodology involves the following two reaction steps: a) introduction of two different polymer segments by the linking reaction of a block copolymer in‐chain anion with a PA‐functionalized polymer and b) regeneration of the PA reaction site. By repeating this reaction sequence, two different polymer segments are advantageously and successively introduced into the μ‐star polymer. In practice, repetition of the reaction sequence affords well‐defined 3‐arm ABC, 5‐arm ABCDE, 7‐arm ABCDEFG, and even 9‐arm ABCDEFGHI μ‐star polymers, composed of polystyrene, polystyrenes substituted with functional groups, polyisoprene, and poly(alkyl methacrylate) arms, respectively.

     

Polymerization of 4‐Methyl‐1,3‐pentadiene with Catalysts Based on Cyclopentadienyl Titanium Chlorides: Effect of anti/syn Isomerism of the Allylic Group on the Chemoselectivity and the Role of Backbiting Coordination in 1,3‐Diene Polymerization

Summary: Homopolymerization of 4‐methyl‐1,3‐pentadiene (MP) and copolymerization of 4‐methyl‐1,3‐pentadiene with alkenes (ethylene, 1‐pentene, 4‐methyl‐1‐pentene) were performed to investigate the effect of the so‐called backbiting coordination on the chemoselectivity of 1,3‐diene polymerization. Three homogeneous catalyst systems were used: CpTiCl₃‐MAO, Cp₂TiCl₂‐MAO and Cp₂TiCl‐MAO. Backbiting coordination is possible with the first catalyst, but not with the other two. The three catalysts gave similar results, which indicates that backbiting has no effect on the polymerization chemoselectivity, contrary to what has been reported in recent literature. An interpretation is presented for the formation of 1,4 units in MP/alkene copolymers. This interpretation is based on the fact that allyl groups have predominantly a syn configuration in MP homopolymerization, whereas allyl groups of anti configuration are formed in MP/alkene copolymerization. The role of backbiting in diene polymerization is discussed.

The effect of anti/syn isomerism on the chemoselectivity in the different polymerizations.     

Photo‐Initiated Living Free Radical Polymerization in the Presence of Dibenzyl Trithiocarbonate

The polymerizations of styrene (St), methyl acrylate (MA), and butyl acrylate (BuA), carried out under UV irradiation at room temperature in the presence of dibenzyl trithiocarbonate (DBTTC) were found to display living free‐radical polymerization characteristics as evidenced by: narrow molecular weight distribution, linear increase of molecular weight with increasing conversion, well‐controlled molecular weight, and first‐order polymerization kinetics. The triblock copolymer, PMA‐PSt‐PMA, with narrow polydispersity and well‐defined structure was successfully prepared using PMA‐S‐C(=S)‐S‐PMA as macro‐photoinitiator under UV irradiation at room temperature. Based on GPC, NMR and FT‐IR analyses, the structures of the polymers were obtained and the mechanism of the polymerization was proposed.     

Living Alternating Copolymerization of a Methylenecyclopropane Derivative with CO to Afford Polyketone with Dihydrophenanthrene‐1,10‐diyl Groups

Summary: Pd complexes prepared from [PdCl(Me)(L)] (L = N‐ligands) and NaBARF catalyze the alternating copolymerization of 7‐methylenedibenzo[a,c]bicyclo[4.1.0]heptane with CO to produce the polyketone. Pd complexes with substituted 1,10‐phenanthroline ligands produce the polymer with narrow molecular weight distribution. Addition of 4‐tert‐butylstyrene to the growing polymer after consumption of the initially charged monomer, results in polymer growth to afford an AB‐type block copolyketone. A Pd complex with an optically active bisoxazoline ligand produces the optically active polymer with narrow polydispersity. The addition of DBU to a solution of polyketone converts the cis‐fused six‐membered rings into the trans‐fused rings via epimerization of the CH carbon attached to the carbonyl group.

Addition of I to cationic Pd complexes catalyzes the ring‐opening copolymerization of the monomer with CO to produce the polyketone, ? (C(?CH₂)? C₁₄H₁₀? CO)_n? ( II ).     

Tailored Semiconducting Polymers: Living Radical Polymerization and NLO‐Functionalization of Triphenylamines

This paper describes the preparation of various polymers with triarylamine side groups. High molecular weight materials were obtained by free radical polymerization utilizing the gel effect. Polymers with a narrow polydispersity and a predetermined molecular weight could be prepared by living radical polymerization. The T_g could, thereby, be controlled between 50 and 140°C either by using different monomers or by varying the molecular weight. Living radical polymerization allowed in addition the preparation of block copolymers. The triarylamine side groups could be transformed into NLO‐chromophores by reaction with tetracyanoethylene. This leads to the incorporation of tricyanoethylene acceptor groups. As this reaction can be performed selectively on one block in block copolymers, microphase separated structures are accessible, which possess charge transport moieties in one phase and NLO‐chromophores in the other phase.     

Unusual Effect of Diethyl Zinc and Triisobutylaluminium in Ethylene/1‐Hexene Copolymerisation using an MgCl2‐Supported Ziegler‐Natta Catalyst

Summary: The use of triisobutylaluminium and diethyl zinc as cocatalyst and chain transfer agent respectively in ethylene/1‐hexene copolymerisation, carried out with a Ziegler‐Natta catalyst of type MgCl₂/TiCl₄/diisobutyl phthalate, has been found to give significantly higher comonomer incorporation than was obtained when triethylaluminium was used in combination with diethyl zinc. Triisobutylaluminium reacts readily with diethyl zinc, yielding metallic zinc, most likely via the formation of intermediate hydride species. In contrast, the use of 2,6‐dimethylpyridine as external donor in this system has been found to have relatively little effect on comonomer incorporation and distribution, indicating that a change from tendentially isospecific to syndiospecific propagation in propene polymerisation is not accompanied by a major improvement in comonomer distribution in ethylene/1‐hexene copolymerisation.

¹H NMR spectrum of the liquid product of the reaction between triisobutylaluminium and diethyl zinc.     

Anionic Polymerization of 1,3‐Cyclohexadiene: Reactivity of Poly(1,3‐cyclohexadienyl)lithium

Summary: The reactivity of poly(1,3‐cyclohexadienyl)lithium (PCHDLi), as a species for the propagation of the anionic polymerization of 1,3‐cyclohexadiene (1,3‐CHD), was examined using a post‐polymerization reaction of PCHDLi and 9‐bromofluorene (9‐BFL). The degree of nucleophilicity of the PCHDLi systems was determined as PCHDLi/1,4‐diazabicyclo[2,2,2]octane (DABCO) > PCHDLi/N,N,N′,N′‐tetramethylethylenediamine (TMEDA) > PCHDLi. The nucleophilicity of PCHDLi was strengthened by the complexation of TMEDA to Li, and was saturated when the TMEDA/Li molar ratio was over 1.0. The rate of polymerization increased with increasing nucleophilicity of PCHDLi. In addition, the molar ratio of the 1,2‐addition (1,2‐CHD unit)/1,4‐addition (1,4‐CHD unit) seemed to be strongly affected by both the nucleophilicity of PCHDLi and the steric hindrance of C? Li bonds in PCHDLi.

Post‐polymerization reaction of poly(1,3‐cyclohexadienyl)lithium (PCHDLi) and 9‐bromofluorene (9‐BFL).